This invention relates to methods and compositions for protecting materials from thermal extremes and from flame. It also relates to methods of making the compositions.
The situation in which it is desirable to protect materials from heat and flame include, for example, protecting static structures such as petroleum storage tanks, chemical production equipment, electrical cable trays, and structural steel from the spread of fire; protecting transportation equipment such as tank cars, aircraft cabins and seat cushions from the same risks; protecting the exterior surfaces of spacecraft and high performance aircraft from heat generated by atmospheric friction; and protecting the nozzles of rocket engines from the heat of propellant gases.
Numerous thermal protective coating materials and systems for applying them are known. Some of the materials are foamed passive insulative materials which protect merely by their low thermal conductivity and their thickness as applied. These include foamed cement or intumesced silicates. Other materials provide active thermal protection. Some intumesce when heated to form a thick closed cell protective layer over the substrate. These include silicate solutions or ammonium phosphate paints or materials such as those disclosed in Nielsen et al., U.S. Pat. No. 2,680,077 or Kaplan, U.S. Pat. No. 3,284,216. Other active thermal protective materials include constituents which sublime at a predetermined temperature, such as those disclosed in Feldman, U.S. Pat. No. 3,022,190. The active thermal protective materials disclosed in Feldman, U.S. Pat. No. 3,849,178 are particularly effective; when subjected to thermal extremes, these materials both undergo an endothermic phase change and expand to form a continuous porosity matrix.
Various methods and structures have also been used or proposed for applying these thermal protective coating materials. The most frequent approach is to apply the materials directly to the substrate, without additional structure. For many applications, however, a reinforcing material, such as fiberglass sheet or a wire mesh, has been embedded in the coating material to strengthen the material and prevent it from cracking or falling off the substrate under conditions of flame or thermal extreme. Examples of this approach are found in Feldman, U.S. Pat. No. 3,022,190, Billing et al, U.S. Pat. No. 3,913,290, Kaplan, U.S. Pat. No. 3,915,777, and Billing et al, U.S. Pat. No. 4,069,075. Sometimes the materials are first applied to a reinforcing structure such as a flexible tape or flexible wire mesh, and the combined structure is applied to the substrate. Examples of this approach are found in Feldman, U.S. Pat. Nos. 3,022,190, Pedlow, 4,018,962, Peterson et al, 4,064,359, Castle, 4,276,332, and Fryer et al,4,292,358. In these last-mentioned systems, the purpose of the reinforcing structure may be both to strengthen the resulting composite and to permit its application to a substrate without directly spraying, troweling or painting the uncured coating materials onto the substrate. In any of the foregoing methods and structures, multiple layers are frequently applied to the substrate to provide additional protection.
Presently known materials and methods, however, are not as efficient, in terms of length of protection for a given weight of protective material, as desirable. Efficiency is particularly important because in many applications weight or volume is critically limited. Moreover, heavily loading coating materials with fire retardants may seriously impair their physical characteristics and otherwise limit their suitability as coatings, for example by limiting their film-forming characteristics or their water-resisting characteristics. Presently known materials are thus frequently limited to certain types of applications.